Fix isort skip config

[cdce8p]

Our current isort config doesn't fully work for the pre-commit hook. Whereas in tox isort is called with the global . path, pre-commit passes all filenames individually.

E.g. running this command will also reformat the mypy/typeshed directory:

pre-commit run isort --all-files

Using skip_glob instead of skip will resolve the issue.
https://pycqa.github.io/isort/docs/configuration/options.html#skip-glob

Followup to #13832 (comment)
/CC: @hauntsaninja

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[hauntsaninja]

Thanks for improving this! :-)